An existing method of paving a surface with a thermoplastic-aggregate membrane involves spray-applying a layer of a thermoplastic material, such as a hot asphalt-rubber mixture, to a surface to be paved, thereby forming a thermoplastic membrane; covering the membrane with a heated layer of aggregate; and rolling (i.e., passing a roller over) the aggregate to embed the aggregate in the membrane.
This prior method has several drawbacks. For example, when the thermoplastic material is asphalt-rubber, in order for the method to be effective, the temperature of the surface to be paved must be at least 13° C. (55° F.) and the atmospheric temperature must be at least 16° C. (60° F.). In tropical climates this is not a major concern, but in cooler climates or in cooler seasons of the year, paving projects can encounter lengthy delays based solely on the weather. In addition, when using this method a danger exists that a paving crew can be sent to a work site and prepare a surface for paving only to encounter a change in temperature due to unexpected cloud movement or the like and be forced to delay construction. In such an instance, crew time, which can cost a paving company approximately $24,000 per day, is wasted.
In addition to the surface and atmospheric temperature requirements, spray-applied asphalt rubber also must meet specific temperature requirements when it is applied to the surface to be paved. The asphalt-rubber mixture must be applied to the surface to be paved at a temperature between 191° C. (375° F.) and 218° C. (425° F.). The mixture may be applied to the roadway immediately following mixing and reacting; however, if it is not used within 6 hours of mixing, the mixture must be allowed to cool below 149° C. (300° F.) for 12 hours, or to ambient temperature for longer periods, and then be uniformly reheated to a temperature between 149° C. (300° F.) and 218° C. (425° F.) (typically between 191° C. (375° F.) and 218° C. (425° F.) at time of placement. Thus, any unexpected delay in construction can severely reduce a paving crew's efficiency.
Following application of an asphalt-rubber layer, the asphalt-rubber material is covered with a heated layer of aggregate which is often precoated with a paving grade or emulsified asphalt. In the existing method, the aggregate must be placed over the asphalt-rubber membrane within 15 minutes after placement of the asphalt-rubber membrane, and must be at a temperature between 127° C. (260° F.) and 163° C. (325° F.). In order to maintain the desired temperature relationship between the asphalt-rubber and the aggregate, initial rolling must commence within 90 seconds following placement of the aggregate in order to embed the aggregate in the asphalt-rubber membrane.